Window Shade Having a Resistance Balancing Mechanism

ABSTRACT

A window shade comprises first and second rails, and a shading structure and a suspension cord connected between the first and second rails. The second rail includes a resistance balancing unit and a cord winding unit to which the suspension cord respectively connects. The resistance balancing unit comprises a housing having an abuttal surface, a pulley pivotally connected with the housing, and a torsion spring. The pulley has a winding portion around which the suspension cord is wrapped, and a shaft portion extending coaxial to the winding portion from a side thereof. The torsion spring is tightly mounted around the shaft portion and has at least one end. The pulley when rotating in one direction drives the end of the torsion spring to push against the abuttal surface of the housing, whereby the torsion spring loosens to allow rotation of the pulley relative to the torsion spring.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority to Taiwan Patent Application No.100127779 filed on Aug. 4, 2011.

BACKGROUND

1. Field of the Invention

The present invention relates to window shades.

2. Description of the Related Art

Many types of window shades are currently available on the market, suchas Venetian blinds, roller shades and honeycomb shades. The shade whenlowered can cover the area of the window frame, which can reduce theamount of light entering the room through the window and providedincreased privacy. A typical window shade can include a top rail, abottom rail, a shading panel and a drive mechanism. The bottom rail isusually connected with a lower end of the shading panel, whereas thedrive mechanism is assembled in the top rail. The drive mechanism caninclude a winding drum, and an operating cord extending outside the toprail. A user can actuate the operating cord to drive rotation of thewinding drum, which can raise or lower the shading panel.

While the use of the operating cord may be convenient for an adult,there is the risk that children strangle on the operating cords.

Therefore, there is a need for a window shade that is convenient tooperate, safer in use and address at least the foregoing issues.

SUMMARY

The present application describes a window shade having a resistancebalancing unit that can be adjusted by raising or lowering an elongatedrail.

In one embodiment, the resistance balancing unit comprises a housinghaving an abuttal surface, a pulley pivotally assembled with thehousing, and a torsion spring. The pulley has a winding portion aroundwhich a suspension cord is wrapped, and a shaft portion extendingcoaxial from a side of the winding portion. The torsion spring istightly mounted around the shaft portion and has at least one end,wherein the pulley when rotating in one direction drives the end of thetorsion spring to push against the abuttal surface of the housing,whereby the torsion spring loosens to allow the pulley to rotaterelative to the torsion spring.

In another embodiment, a window shade is described. The window shadecomprises a first rail, a second rail, a shading structure disposedbetween the first rail and the second rail, and at least a suspensioncord connected between the first and second rails. The second railincludes a resistance balancing unit and a cord winding unit, thesuspension cord respectively connecting with the resistance balancingunit and the cord winding unit. The resistance balancing unit comprisesa housing having an abuttal surface, a pulley pivotally connected withthe housing, and a torsion spring. The pulley has a winding portionaround which a suspension cord is wrapped, and a shaft portion extendingcoaxial from a side of the winding portion. The torsion spring istightly mounted around the shaft portion and has at least one end,wherein the pulley when rotating in one direction drives the end of thetorsion spring to push against the abuttal surface of the housing,whereby the torsion spring loosens to allow the pulley to rotaterelative to the torsion spring.

At least one advantage of the window shades described herein is theability to conveniently adjust the shade by raising and lowering thelower rail. Moreover, the assembly of the resistance balancing unit inthe window shade can allow to accurately hold the shading structure atany height.

The foregoing is a summary and shall not be construed to limit the scopeof the claims. The operations and structures disclosed herein may beimplemented in a number of ways, and such changes and modifications maybe made without departing from this invention and its broader aspects.Other aspects, inventive features, and advantages of the invention, asdefined solely by the claims, are described in the non-limiting detaileddescription set forth below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating an embodiment of a window shadein a downwardly deployed stage;

FIG. 2 is a schematic view illustrating the window shade in an upwardlyretracting stage;

FIG. 3 is a perspective view of a resistance balancing unit assembled inthe window shade shown in FIG. 1;

FIG. 4 is a cross-sectional view taken along section C1 shown in FIG. 3;

FIG. 5 is a cross-sectional view taken along section C2 shown in FIG. 3;

FIG. 6 is a bottom view of the resistance balancing unit;

FIG. 7 is a front view illustrating a cord winding unit assembled in thewindow shade shown in FIG. 1;

FIG. 8 is a top view of the cord winding unit shown in FIG. 7;

FIG. 9 is a partial cross-sectional view of the cord winding unit;

FIG. 10 is a perspective view of the resistance balancing unit as thesecond rail is adjusted toward the first rail;

FIG. 11 is a cross-sectional view taken along section C1 shown in FIG.10;

FIG. 12 is a cross-sectional view taken along section C2 shown in FIG.10;

FIG. 13 is a schematic view illustrating another embodiment of a controlmodule associating a resistance balancing unit with a cord winding unit;

FIG. 14 is a schematic view detailing the construction of the cordwinding unit shown in FIG. 13;

FIG. 15 is a schematic view illustrating a window shade provided withthe resistance balancing unit and the cord winding unit shown in FIG.13;

FIG. 16 is a schematic view illustrating the window shade shown in FIG.15 adjusted upward;

FIG. 17 is a cross-sectional view illustrating another embodiment of aresistance balancing unit;

FIG. 18 is a bottom view of the resistance balancing unit shown in FIG.17; and

FIG. 19 is a schematic view illustrating another variant embodiment of aresistance balancing unit.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIGS. 1 and 2 are schematic views illustrating one embodiment of ahand-pull type window shade 100. More particularly, FIG. 1 shows thewindow shade 100 in a downwardly deployed state, and FIG. 2 shows thewindow shade 100 in an upwardly retracting state. The window shade 100can include a first rail 102, a second rail 104, a shading structure106, suspension cords 108, resistance balancing units 110 and a cordwinding unit 112. The shading structure 106 can have upper and lowerends respectively affixed with the first rail 102 and the second rail104. The resistance balancing units 110 and the cord winding unit 112can be respectively installed in the second rail 104. In one embodiment,two resistance balancing units 110 and one cord winding unit 112 can beprovided to form a control module of the window shade 100, the cordwinding unit 112 being installed between and spaced apart from the tworesistance balancing units 110. Each of the suspension cords 108 canhave a first end fixedly attached with the first rail 102, and anopposite second portion respectively passing through the resistancebalancing units 110 and connected with the cord winding unit 112. Thecord winding unit 112 can have a spring-driven mechanism that can beoperable to wind the suspension cords 108 when the second rail 104rises. Once the second rail 104 reaches and is released at a desiredheight, all of the applied forces including the spring force from thecord winding unit 112, the weights of the shading structure 106 and thesecond rail 104, and internal friction forces (including the resistiveforce generated by the resistance balancing unit 110), can be balancedto create an equilibrium condition. As a result, the second rail 104 canbe held stationary at the desired height.

In one embodiment, the first rail 102 can be affixed with a top portionof a window opening frame, and the second rail 104 provided with theresistance balancing units 110 and the cord winding unit 112 can besuspended vertically from the first rail 102. In alternate embodiments,the positions of the first and second rails can also be interchanged:the second rail 104 provided with the resistance balancing units 110 andthe cord winding unit 112 can be affixed with a top portion of a windowopening frame, whereas the first rail 102 can be suspended verticallyfrom the second rail 104.

Referring again to FIGS. 1 and 2, the shading structure 106 can be madeof a fabric material, e.g., honeycomb structure formed from a fabricmaterial. In alternate embodiments, the shading structure 106 can alsohave other types of constructions, e.g., slats, shading rows, etc.

FIG. 3 is a perspective view of the resistance balancing unit 110, FIG.4 is a cross-sectional view taken along section C1 shown in FIG. 3, FIG.5 is a cross-sectional view taken along section C2 shown in FIG. 3, andFIG. 6 is a bottom view of the resistance balancing unit 110. As shownin FIGS. 3-6, the resistance balancing unit 110 can include a housing114, a pulley 116, a torsion spring 118 and a movable blade 120. Thehousing 114 can have a generally rectangular shape, including a firstface 114A and a second face 114B. In the illustrated embodiment, thefirst face 114A and the second face 114B can be exemplary perpendicularto each other. The first face 114A can have a hole 122. The second face114B can be formed with a slotted window 124 where the blade 120 ismovably assembled, and a slit 126 can be defined between the blade 120and a side edge 124A of the window 124 for passage of the suspensioncord 108.

Moreover, an interior of the housing 114 can define a first receivingspace 128A and a second receiving space 128B that are at least partiallyseparated from each other by a sidewall 130. The first receiving space128A can respectively communicate with the hole 122 and the slit 126.

The pulley 116 can include a winding portion 116A and a shaft extension116B. The shaft extension 116B can project from a side of the windingportion 116A along a same axis of rotation. In one embodiment, thewinding portion 116A and the shaft extension 116B can be formedintegrally with the pulley 116. When the pulley 116 is pivotallyassembled with the housing 114, the winding portion 116A can be placedin the first receiving space 128A, and the shaft extension 116B can passthrough an opening of the sidewall 130 and be disposed in the secondreceiving space 128B. Accordingly, when the pulley 116 rotates relativeto the housing 114, the winding portion 116A and the shaft extension116B can rotate in unison about a same axis.

The torsion spring 118 can be tightly mounted on an outer peripheralsurface of the shaft extension 116B. In one embodiment, the torsionspring 118 can be exemplary a bidirectional torsion spring. Twoprotruding ends 118A and 118B of the torsion spring 118 can berespectively disposed adjacent to two abuttal surfaces 132 of thehousing 114 adjacent to the second receiving space 128B.

The suspension cord 108 can travel into the first receiving space 128Athrough the hole 122 of the first face 114A, wrap about one and halfturn around the winding portion 116A, and extend outside the housing 114via the slit 126 on the second face 114B. Accordingly, a first portion108A of the suspension cord 108 outwardly adjacent to the first face114A can be substantially perpendicular to a second portion 108B of thesuspension cord 108 outwardly adjacent to the second face 114B.Moreover, owing to the pressure applied by the blade 120, the secondportion 108B of the suspension cord 108 passing through the slit 126 canbe kept in contact with the blade 120 and the side edge 124A of thewindow 124. It is worth noting that because the suspension cord 108 canbe wrapped several turns around the pulley 116 (in particular at leastone or more turn), the contact area between the suspension cord 108 andthe pulley 116 can be increased, which can create suitable frictionalresistance to balance other forces exerted on the second rail 104. As aresult, the second rail 104 can be kept stationary at any height in astable manner.

FIGS. 7 and 8 are respectively front and top views illustrating the cordwinding unit 112, and FIG. 9 is a partial cross-sectional view of thecord winding unit 112. The cord winding unit 112 can include a casing140, two winding drums 142, two coil springs 143 and two guide rollers144. Two opposite sides of the casing 140 can respectively includeopenings 146 and 148 for the passage of the two suspension cords 108.The two guide rollers 144 can be movably assembled with two shaftportions 145 adjacent to the openings 146 and 148, respectively.Accordingly, each guide roller 144 can slide along the associated shaftportion 145.

Each of the winding drums 142 can be pivotally connected with the casing140. An upper end of each winding drum 142 can be affixed with a gear150. The pivot axes of the winding drums 142 can be parallel to theshaft portions 145, and substantially perpendicular to the pivot axis ofthe pulley 116. Moreover, the casing 140 can also be pivotally connectedwith a pivot shaft 152 disposed between the two winding drums 142. Thepivot shaft 152 can be substantially parallel to the pivot axes of thewinding drums 142, and can have an upper end affixed with a transmissiongear 154. The transmission gear 154 can be respectively engaged with thegears 150 of the winding drums 142, whereby the winding drums 142 canrotate in unison to concurrently wind or unwind the suspension cords108.

Pressing arms 156 can be respectively mounted adjacent to the windingdrums 142, and can act to ensure that the suspension cords 108 are woundtightly around the winding drums 142. Each of the pressing arms 156 canhave a first end pivotally connected with the casing 140, and a secondend that presses the corresponding suspension cord 108 against thesurface of the winding drum 142. As each suspension cord 108progressively winds around the associated winding drum 142, the pressingarm 156 can pivotally displace for adjustment.

As shown in FIG. 9, the coiled springs 143 can be respectively assembledin the winding drums 142. Each of the coiled springs 143 can have afirst end anchored with the casing 140, and a second end connected withthe associated winding drum 142. The coiled springs 143 can respectivelybias the winding drums 142 to rotate in directions for winding thesuspension cords 108.

When the cord winding unit 112 is assembled, the two suspension cords108 can respectively travel into the casing 140 via the openings 146 and148, wrap around the two guide rollers 144, and then connect and wind onthe two winding drums 142. Biased by the coiled springs 143, the windingdrums 142 can rotate to wind the suspension cords 108. While the windingdrums 142 are winding the suspension cords 108, the guide rollers 144can respectively slide along the shaft portions 145 so that thesuspension cords 108 can be respectively wound in turns uniformlydistributed on the surfaces of the winding drums 142.

Exemplary operation of the window shade 100 is described hereafter withreference to FIGS. 1-11. First referring to FIGS. 1 and 3-9, the secondrail 104 can be pulled downward in a direction F1 (i.e., in a directionthat increases the distance between the first rail 102 and the secondrail 104), which causes each suspension cord 108 to unwind from theassociated winding drum 142 and drives the winding drum 142 in rotation.As it unwinds from the winding drum 142, the suspension cord 108 candrive the pulley 116 to rotate in a direction (e.g., in theanticlockwise direction shown in FIG. 5) to push the end 118A of thetorsion spring 118 against the abuttal surface 132. As a result, thetorsion spring 118 initially in a tightened state can loosen to permitrotation of the pulley 116 relative to the torsion spring 118.Accordingly, the length of the suspension cords 108 between the firstand second rails 102 and 104 can progressively increase.

When the user stops pulling the second rail 104 downward (i.e., thefirst and second rails 102 and 104 are stationary), each torsion spring118 can recover a tightened state on the associated pulley 116. As aresult, the pulleys 116 no longer rotate, and a frictional resistancecan be created owing to the wrapping of the suspension cords 108 aroundthe pulleys 116. Accordingly, the spring forces exerted by the coiledsprings 143 on the winding drums 142 can counterbalance the weightapplied on the second rail 104, the resistance generated by theresistance balancing units 110, and other internal frictional forces tostop the winding drums 142. Owing to the balance of all the forcesapplied thereon, the second rail 104 can be kept stationary at thedesired position in a stable manner.

As shown in FIG. 2, when the second rail 104 is moved upward in adirection F2 (i.e., in the direction that reduces the distance betweenthe first and second rails 102 and 104), the portions of the suspensioncords 108 between the first and second rails 102 and 104 can becomeloose (i.e., forming a slack). As a result, the winding drums 142 of thecord winding unit 112 can reversely rotate to wind the suspension cords108.

In conjunction with FIG. 2, FIGS. 10-12 are schematic views illustratingintermediary stages of the resistance balancing unit 110 during anupward displacement of the second rail 104. More particularly, FIG. 10is a perspective view of the resistance balancing unit 110, FIG. 11 is across-sectional view taken along section C1 shown in FIG. 10, and FIG.12 is a cross-sectional view taken along section C2 shown in FIG. 10. Asthe winding drum 142 is winding the suspension cord 108, the pressurefrom the blade 120 can keep the portion of the suspension cord 108 thatis located between the resistance balancing unit 110 and the cordwinding unit 112 in a tensioned state. Accordingly, the suspension cord108 can smoothly slip around the pulley 116, and be wound around thewinding drum 142 without being interlaced. The length of the suspensioncords 108 between the first and second rails 102 and 104 thus canprogressively shorten.

When the user stops moving the second rail 104 upward, each torsionspring 118 can recover a tightened state on the associated pulley 116.As a result, each of the pulleys 116 is stopped, and a frictionalresistance is created owing to an increased contact area between thesuspension cord 108 and the pulley 116. Accordingly, the spring forcesexerted by the coiled springs 143 on the winding drums 142 cancounterbalance the weight applied on the second rail 104, the resistancegenerated by the resistance balancing units 110 and other internalfrictional forces to stop the winding drums 142. Owing to the balance ofall the forces applied thereon, the second rail 104 can be keptstationary at the desired position in a stable manner.

With the aforementioned construction, the second rail 104 can be heldstationary at any position. Even if the second rail 104 is adjusted toreach a limit of the working range of the coiled springs 143, theresistance balancing units 110 can still create proper resistance thatcan balance the spring force of the cord winding unit 112 such that theoperation of the window shade 100 can be facilitated, and the secondrail 104 kept be stationary in an equilibrium condition at any heights.Aside the aforementioned embodiments, the resistance balancing unit canalso be associated with other constructions of the cord winding unit.

FIG. 13 is a schematic view illustrating another embodiment associatinga resistance balancing unit 210 with a cord winding unit 212, and FIG.14 is a schematic view detailing the construction of the cord windingunit 212. As shown in FIG. 13, the resistance balancing unit 210 can beassociated with the cord winding unit 212 to form a control module. Theresistance balancing unit 210 can be similar in construction to theresistance balancing unit 110 of the previous embodiment, including ahousing 214, a rotary pulley 216 and a torsion spring 218. The pulley216 can be pivotally assembled with the housing 214, and can include awinding portion 216A and a shaft extension 216B. The shaft extension216B can project from a side of the winding portion 216A along a sameaxis of rotation.

The torsion spring 218 can be tightly mounted on an outer peripheralsurface of the shaft extension 216B. Two protruding ends 218A and 218Bof the torsion spring 218 can be respectively disposed adjacent to twoabuttal surfaces 232 of the housing 214.

The suspension cord 108 can enter the resistance balancing unit 210 froma first face thereof, wrap about one and half turn around the windingportion 216A, and extend outward from a second face of the resistancebalancing unit 210. Accordingly, a first portion of the suspension cord108 outwardly adjacent to the first face of the resistance balancingunit 210 can extend in a direction different from a second portion ofthe suspension cord 108 outwardly adjacent to the second face of theresistance balancing unit 210.

Referring to FIGS. 13 and 14, the cord winding unit 212 can include acasing 240. A side of the casing 240 can be provided with an extendingplate 240A for affixing the resistance balancing unit 210. Thesuspension cord 108 can pass through the resistance balancing unit 210,and then travel into the casing 240 via a hole 242 to connect with oneor more part inside the cord winding unit 212.

As shown in FIG. 14, the cord winding unit 212 can include a windingdrum 244 and a coiled spring 246 mounted inside the casing 240. A sideof the winding drum 244 can be connected with a hollow shaft portion248. The winding drum 244 and the shaft portion 248 can be formedintegral in a single body, or can be separate parts assembled together.The casing 240 can have an interior in which are defined a firstreceiving space 240B and a second receiving space 240C. The winding drum244 can be disposed in the first receiving space 240B, and the shaftportion 248 can be disposed in the second receiving space 240C, suchthat the winding drum 244 and the shaft portion 248 can rotate about asame axis relative to the casing 240. Moreover, when the cord windingunit 212 is assembled with a window shade, a transmission axle 310(shown with dotted lines) can pass through the winding drum 244 and theshaft portion 248, whereby multiple cord winding units can be drivenconcurrently via the transmission axle 310.

The coiled spring 246 can be installed around the shaft portion 248 inthe second receiving space 240C. The coiled spring 246 can have a firstend connected with the shaft portion 248, and a second end connectedwith the casing 240.

The suspension cord 108 can travel through the hole 242, and extend intothe first receiving space 240B to connect with the winding drum 244. Thewinding drum 244 can be biased in rotation by the coiled spring 246 forwinding the suspension cord 108.

In conjunction with FIGS. 13 and 14, FIG. 15 is a schematic viewillustrating a window shade 300 provided with the resistance balancingunit 210 and the cord winding unit 212. The window shade 300 can includea first rail 302, a second rail 304 provided with the resistancebalancing unit 210 and the cord winding unit 212, and a shadingstructure 306 connected between the first and second rails 302 and 304.The second rail 304 can be affixed with a top of a window frame, and thefirst rail 302 can be suspended vertically from the second rail 304.

The second rail 304 can include a transmission axle 310, and a pluralityof resistance balancing units 210 and cord winding units 212. Thetransmission axle 310 can be assembled through the casing 240, the shaftportion 248 and the winding drum 244 of each cord winding unit 212, andthereby define a same axis of rotation about which the shaft portions248 and the winding drums 244 of the cord winding units 212 can rotatein unison.

The suspension cords 108 (shown with dotted lines) can be respectivelyconnected between the cord winding units 212 and the first rail 302.More specifically, each of the suspension cords 108 can have a first endconnected with the winding drum 244 of one cord winding unit 212, and asecond end securely affixed with the first rail 302.

Like the embodiments previously described, when the first rail 302 islowered, each suspension cord 108 can unwind from the associated windingdrum 244 which is driven in rotation. As it unwinds from the windingdrum 244, the suspension cord 108 can drive the pulley 216 in rotation,which causes the end 218A of the torsion spring 218 to push against theabuttal surface 232. As a result, the torsion spring 218 previously in atightened state can loosen, such that the pulley 216 can rotate relativeto the torsion spring 218. When the user stops lowering the first rail302, the torsion spring 218 can recover its tightened state on thepulley 216. As a result, the pulley 216 no longer rotates, and theincreased contact area between the suspension cord 108 and the pulley216 can create frictional resistance. Accordingly, the total springforce exerted by the coiled springs 246 on the winding drums 244 cancounterbalance the weight applied on the first rail 302, the resistancecreated by the resistance balancing units 210, and frictional forcesexerted by other internal parts. The winding drums 244 can thereby stoprotating, and the first rail 302 can be sustained at the desired heightin equilibrium.

As shown in FIG. 16, when the first rail 302 is raised, the suspensioncords 108 between the first rail 302 and the second rail 304 can becomeloose (i.e., form a slack). Accordingly, the winding drum 244 of eachcord winding unit 212 can reversely rotate to wind the associatedsuspension cord 108. When the user stops raising the first rail 302, thetorsion springs 218 can respectively tighten on the pulleys 216. As aresult, each of the pulleys 216 can stop rotating, and the increasedcontact area between each suspension cord 108 and the associated pulley216 can create frictional resistance. Accordingly, the total springforce exerted by the coiled springs 246 on the winding drums 244 cancounterbalance the weight applied on the first rail 302, the resistancecreated by the resistance balancing units 210, and frictional forcesexerted by other internal parts. The winding drums 244 can thereby stoprotating, and the first rail 302 can be sustained at the desired heightin equilibrium.

The resistance balancing units described previously can also beimplemented with other constructions. For example, while the resistancebalancing unit has been described as using a bidirectional torsionspring, other embodiments of the resistance balancing unit can also usea unidirectional torsion spring. A variant embodiment of the resistancebalancing unit is exemplary described hereafter with reference to FIGS.17 and 18.

FIG. 17 is a cross-sectional view illustrating another construction of aresistance balancing unit 410, and FIG. 18 is a bottom view of theresistance balancing unit 410. The resistance balancing unit 410 can besimilar to the previous embodiment in construction, including a housing414, a pulley 416, a torsion spring 418 and a movable blade 420. Thepulley 416 can be pivotally assembled with the housing 414, and caninclude a winding portion 416A and a shaft extension 416B. The shaftextension 416B can project from a side of the winding portion 416A alonga same axis of rotation. The torsion spring 418 can be a unidirectionaltorsion spring having an end 418A. The torsion spring 418 can be tightlymounted on an outer peripheral surface of the shaft extension 416B, andthe end 418A can be anchored with the housing 414. The suspension cord108 can enter the resistance balancing unit 410 from a first face 414A,wrap about one and half turn around the winding portion 416A, travelpast the blade 420, and extend outward from a second face 414B of theresistance balancing unit 410.

The operation of the resistance balancing unit 410 can be similar to theprevious embodiments. When the second rail (i.e., the rail suspendedfrom the first rail) is lowered, each stretched suspension cord 108 candrive rotation of the associated pulley 416, which causes the torsionspring 418 previously tightening on the pulley 416 to loosen.Accordingly, the pulleys 416 can respectively rotate relative to thetorsion springs 418, and the suspension cords 108 extending between thefirst and second rails can lengthen. When the user stops lowering thesecond rail (i.e., the first and second rails become stationary), thetorsion springs 418 can respectively tighten on the pulleys 416. As aresult, the pulleys 416 stop rotating, and the wrap of the suspensioncords 108 around the pulleys 416 can create frictional resistance, whichcan act to balance all of the forces exerted on the second rail.Accordingly, the second rail can be sustained at the desired position inequilibrium.

While the aforementioned embodiment has the resistance balancing unitarranged at a turn position of the suspension cord 108, it will beappreciated that the resistance balancing unit can also be used at otherlocations. For example, as shown in FIG. 19, the suspension cord 108 canturn around the a pulley 502, enter the resistance balancing unit 510from a first face 514A thereof, wrap about one turn around the pulley516, travel past the movable blade 520, exit the resistance balancingunit 510 via a second face 514B thereof, and then connect with the cordwinding unit 112/212. Like previously described, the resistancebalancing unit 510 can include a torsion spring tightly mounted aroundthe pulley 516 (not shown). The second side 514B and the first side 514Acan be substantially parallel to each other, such that the portions ofthe suspension cord 108 respectively entering and exiting the resistancebalancing unit 510 can be parallel to a same direction.

The window shades described herein do not have any operating cords, andcan be conveniently adjusted by raising and lowering the lower rail.Accordingly, the risk of children strangling on operating cords from thewindow shade can be prevented. Moreover, the assembly of the resistancebalancing unit can allow to accurately hold the shading structure inequilibrium at any heights.

Realizations in accordance with the present invention therefore havebeen described only in the context of particular embodiments. Theseembodiments are meant to be illustrative and not limiting. Manyvariations, modifications, additions, and improvements are possible.Accordingly, plural instances may be provided for components describedherein as a single instance. Structures and functionality presented asdiscrete components in the exemplary configurations may be implementedas a combined structure or component. These and other variations,modifications, additions, and improvements may fall within the scope ofthe invention as defined in the claims that follow.

1. A resistance balancing unit suitable for use with a window shade,comprising: a housing having an abuttal surface; a pulley pivotallyassembled with the housing, the pulley having a winding portion aroundwhich a suspension cord is wrapped, and a shaft portion extendingcoaxial from a side of the winding portion; and a torsion spring tightlymounted around the shaft portion and having at least one end, whereinthe pulley when rotating in one direction drives the end of the torsionspring to push against the abuttal surface of the housing, whereby thetorsion spring loosens to allow the pulley to rotate relative to thetorsion spring.
 2. The resistance balancing unit according to claim 1,wherein the housing has a first face and a second face, the suspensioncord entering the housing from the first face, wrapping around thewinding portion, and extending outside the housing from the second face.3. The resistance balancing unit according to claim 2, wherein the firstface and the second face are substantially perpendicular to each other.4. The resistance balancing unit according to claim 2, wherein the firstface and the second face are substantially parallel to each other. 5.The resistance balancing unit according to claim 2, wherein the housingincludes a blade assembled at the second face, the blade and an edge ofthe housing defining a slit for passage of the suspension cord.
 6. Theresistance balancing unit according to claim 5, wherein the blade ismovably assembled with the housing, and is operable to press against thesuspension cord.
 7. The resistance balancing unit according to claim 1,wherein the suspension cord wraps around the pulley about one or moreturn.
 8. A window shade comprising: a first rail; a second rail; ashading structure disposed between the first rail and the second rail;and at least a suspension cord connected between the first and secondrails; wherein the second rail includes a resistance balancing unit anda cord winding unit, the suspension cord respectively connecting withthe resistance balancing unit and the cord winding unit, the resistancebalancing unit comprising: a housing having an abuttal surface; a pulleypivotally connected with the housing, the pulley having a windingportion around which a suspension cord is wrapped, and a shaft portionextending coaxial from a side of the winding portion; and a torsionspring tightly mounted around the shaft portion and having at least oneend, wherein the pulley when rotating in one direction drives the end ofthe torsion spring to push against the abuttal surface of the housing,whereby the torsion spring loosens to allow the pulley to rotaterelative to the torsion spring.
 9. The window shade according to claim8, wherein the housing has a first face and a second face, thesuspension cord enters the housing from the first face, wraps around thewinding portion, and extends outside the housing via the second face.10. The window shade according to claim 9, wherein the first face andthe second face are substantially perpendicular to each other.
 11. Thewindow shade according to claim 9, wherein the first face and the secondface are substantially parallel to each other.
 12. The window shadeaccording to claim 9, wherein the housing includes a blade assembled atthe second face, the blade and an edge of the housing defining a slitfor passage of the suspension cord.
 13. The window shade according toclaim 12, wherein the blade is movably assembled with the housing, andis operable to press against the suspension cord.
 14. The window shadeaccording to claim 8, wherein the suspension cord wraps around thepulley about one or more turn.
 15. The window shade according to claim8, wherein an adjustment that increases a distance between the first andsecond rails causes the suspension cord to unwind from the cord windingunit and drives the pulley in rotation, which results in the end of thetorsion spring to push against the abuttal surface, whereby the torsionspring is loosened and the pulley is allowed to rotate relative to thetorsion spring.
 16. The window shade according to claim 8, wherein anadjustment that reduces a distance between the first and second railscauses the suspension cord between the first and second rails to becomeloose, which results in the cord winding unit to wind the suspensioncord under a spring force.
 17. The window shade according to claim 8,wherein the torsion spring recovers a tightened state on the pulley tostop the pulley when the first and second rails are stationary.
 18. Thewindow shade according to claim 8, wherein the resistance balancing unitis spaced apart from the cord winding unit.
 19. The window shadeaccording to claim 8, wherein the cord winding unit includes a casing, awinding drum, a coiled spring connected with the winding drum, and aguide roller movable along a shaft portion, the guide roller slidingalong the shaft portion to facilitate uniform winding of the suspensioncord on the winding drum during an adjustment that reduces a distancebetween the first and second rails.